Electrical insulating member such as a distributor cap

ABSTRACT

A hollow insulating member has a wall which consists of two layers, one of which at least partly surrounds the other. One of these layers is composed of an electrically insulating substance whereas the other of these layers is composed of a thermally insulating foam material. Air is entrapped in the foam material, and may also be entrapped in an air gap between the two layers.

United States Patent Anselment et al.

1 Sept. 24, 1974 ELECTRICAL INSULATING MEMBER SUCH AS A DISTRIBUTOR CAPInventors: Wolfgang Anselment; Walter Holl,

both of Stuttgart, Germany Assignee: Robert Bosch GmbH, Stuttgart,

Germany Filed: Sept. 11, 1973 Appl. No.: 396,193

Foreign Application Priority Data Sept. 12, 1972 Germany 2244583 US. Cl174/138 F, 174/209, 200/19 WG Int. CL. HOlr 39/60, l-lOlh 19/06, HOlb17/60 Field of Search 174/77 S, 110 F, 138 F, 174/139, 209; 123/143 C,146.5 R, 146.5 A, 169 P, 169 PA, 169 PH; 200/19 DC, 19 DR, 19 WG, 168 G;220/9 F; 339/26, 116 R References Cited UNITED STATES PATENTS 2/1957Ebel et a1. 174/110 F UX 3,009,986 11/1961 Stephens 174/138 F X3,037,652 6/1962 Wa1lace....-

220/9 F X 3,243,504 3/1966 Johnson 174/138 F 3,625,785 12/1971 Loberodet a1 220/9 F X FOREIGN PATENTS OR APPLICATIONS 1,932,127 1/1971 Germany123/1465 R 2,011,242 9/1971 Germany 123/1465 A Primary Examiner-LaramieE. Askin Attorney, Agent, or Firm-Michael S. Striker A hollow insulatingmember has a wall which consists of two layers, one of which at leastpartly surrounds the other. One of these layers is composed of anelectrically insulating substance whereas the other of these layers iscomposed of a thermally insulating foam material. Air is entrapped inthe foam material, and may also be entrapped in an air gap between thetwo layers.

ABSTRACT 15 Claims, 2 Drawing Figures ELECTRICAL INSULATING MEMBER SUCHAS A DISTRIBUTOR CAP BACKGROUND OF THE INVENTION The invention relatesgenerally to insulators or insulating members. More particularly, theinvention relates to hollow insulators which are adapted to receive acurrent-conducting lead and the wall or walls of which have electricallyinsulating properties. Of special interest are distributor caps whichare adapted to receive a current-conducting lead connected to theignition system of a combustion engine.

The electrically insulating walls of the known articles of the typeunder discussion are composed of a solid or dense substance, and thebase material for the latter is advantageously a polyester resin. Thisparticular base material is used because of its good electricalinsulating properties. However, if a known article of this type is used,for example, in the motor of a motor vehicle, to seal or enclose a spacetherein and a large amount of heat is generated, then, if the article iscooled from exteriorly thereof, e.g., due to atmospheric changes, due towater being sprayed thereon or the like, condensation of water takesplace on the inner surfaces of the walls of the article. If thiscondensed water comes into contact with dirt particles or with thenitric oxide produced by electrical sparks, creepage or leakage pathsmay form, i.e., paths along which electrical current will flowpreferentially. Such leakage paths decrease the electrical insulatingproperties of the article and even- SUMMARY OF THE INVENTION It is,accordingly, a general object of the invention to provide a novelinsulator.

More particularly, it is an object of the invention to.

provide a hollow insulating member of the type under discussion whichsatisfactorily avoids the abovementioned shortcomings associated withthe known constructions.

Still more specifically, it is an object of the invention to provide ahollow insulating member of the type under discussion, wherein thecondensation of water is at least minimized.

In accordance with these and other objects, the invention provides, as anovel article of manufacture, a hollow insulating member, particularly adistributor cap adapted to receive at least one current-conducting leadconnected to the ignition system of a combustion engine, which comprisesa wall having a first layer composed of an electrically insulatingsubstance, and a second layer composed of a thermally insulatingmaterial. One of the layers surrounds at least a portion of the other ofthe layers and the wall has at least one body of air entrapped therein.

The first and second layers may be fast with one another. Due to theprovision of a thermally insulating layer, the degree of watercondensation on the inner surface or surfaces of the novel article whenthe latter is heated and a cold substance is applied to the outersurface or surfaces of the same, is substantially less than in the knownconstructions.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view, partly insection, of a distributor cap according to one embodiment of theinvention; and

FIG. 2 is a view similar to FIG. 1, but showing another embodiment ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For purposes of thisspecification, the invention will be described with reference to adistributor cap, i.e., to the cap of a distributor which is used in theelectrical ignition system of a motor vehicle. It is to be understood,however, that this is in no way intended to limit the invention to suchan application only. A

Referring now to FIG. 1, the cap of a non-illustrated distributor isindicated generally at I. The wall of the cap 1 comprises anelectrically insulating layer 2, that is, the layer 2 is of anelectrically insulating substance. The layer 2 issubstantiallycup-shaped and is composed of a dense substance. Advantageously,although not necessarily, the material of the layer 2 is a polyesterresin. The layer 2 may have a thickness of substantially 2 to 4millimeters, a currently preferred thickness being about 3 millimeters.

The cap 1 has a tubular wall portion and another wall portion whichextends transversely to the axis of the tubular wall portion so that thecap I has the form of a hollow body. The transverse wall portion isprovided with tubular projections 3, 4, 5, 6 and 7 each of which isadapted to receive a non-illustrated currentconducting lead. The middleprojection 3 is adapted to receive a lead connected to the ignition coilprovided in the ignition system of a combustion engine and to which theignition voltage derived from the secondary winding of the ignition coilis supplied. On the other hand, each of the projections 4, 5, 6 and 7 isadapted to receive a lead which distributes the ignition voltage to thespark plugs provided in the respective cylinders of the combustionengine. For the sake of clarity, the component parts of the combustionengine have not been illustrated here. The projections 3, 4, 5, 6 and 7may be formed integrally with the cap 1 if desired, and this is the casein the embodiment shown in FIG. 1.

In order to prevent, or at least substantially reduce, the condensationof water on the inner surface or surfaces of the cap 1, the wall of thecap 1 is further provided with a heat or thermally insulating sleeve orjacket 8. In the exemplary embodiment of FIG. 1, the sleeve 8 is shownas being in the form of a layer 9 composed of a foam material. The layer9, which may be fast with or connected with the layers 2, is illustratedhere as being provided exteriorly of the layer 2 although it might alsobe provided interiorly thereof. It may be seen that the layer 9surrounds at least a portion of the layer 2. The layer 9 may be providedon the layer 2 in simple fashion by selecting for the layer 9 a hardfoam which, during production of the cap 1, may be formed as a coatingon the exterior of the electrically insulating layer 2 by spraying orinjection molding. It is preferable to use a closed-cell hard foam (afoam material wherein the cells do not communicate with one another) or,at least, a hard foam having a substantially non-porous outer surface.The reason is to prevent penetration of dirt and moisture into the cellsof the foam material, since this could destroy the effectiveness of thelayer 9 as a thermal insulator. It has been found that a polyurethanefoam is particularly, although not exclusively, suitable for thispurpose.

It is self-understood that, instead of providing the cap 1 with ahardened layer 9 of a foam material which is fixedly secured thereto,the layer 9 of the thermally insulating sleeve 8 may also be composed ofan elastic material. An elastic foam material such as, for example, foamrubber, is especially suitable in such an instance, although otherelastic materials may also be used. When the sleeve 8 comprises anelastic material, the sleeve 8 may be fastened to or connected with thecap 1 by providing the former with a shape which corresponds to that ofthe cap 1 but choosing the inner dimensions of the sleeve 8 to besmaller than the outer dimensions of the layer 2. By then prestressingthe sleeve 8, placing the same over the layer 2 and the pro jections 3,4, 5, 6 and 7 and then releasing the tension, the sleeve 8 is held in anexpanded state by the layer 2 and thereby caused to elastically bearagainst the same. This type of construction of the sleeve 8 has theadvantage that it may be subsequently provided on distributors whichhave already been mounted, whenever desired.

The use of foam (i.e., cellular) material for the layer 9 is highlyadvantageous, because the body of air entrapped in the totality of cellsof the layer 9 acts as a very efficient insulator. Evidently, theemployment of the layer 9 makes it possible to make the layer 2 oflesser thickness, since the layer 2 now exclusively has an electricallyinsulating function, and thus to save material and reduce manufacturingexpenses. Moreover, the cap 1 can now also be lighter in weight, aconsideration which may be of importance in some circumstances.

The embodiment of FIG. 2 is largely similar to that of FIG. l, and likereference numerals have been used to designate like elements.

The essential difference here is that the layer 10, which replaces thelayer 9 of FIG. 1, is spaced from the layer 2 and defines with the samean airgap 11. The layer 10 may be of rigid synthetic plastic material,for example of solid (non-foamed) polyester, of polyester orpolypropylene foam, or rigid polyurethane foam having a non-cellularintegral skin. Openings 12 are provided, through which the tubularportions 3, 4, 5, 6 and 7 extend to the exterior of layer 10.

In this embodiment, the body of air entrapped in the gap 11 providesexcellent thermal insulating properties, which are further improved ifthe layer 10 is of foam material and thus contains additional air whichis entrapped in its cells.

In this embodiment, also, the layer 10 can be applied subsequently to analready mounted distributor. For this purpose, the layers 2 and 10 arereleasably connected, the layer 10 being provided with the illustratedradially inwardly extending projections 14, which are located betweenrespective circumferentially spaced axial slots 13 and which each snapbehind a bevel 15 provided on the layer 2 at the open side of the cap 1.

In the region of the open side of the cap 1, the layer 10 has a portionof enlarged inner diameter. The shoulder 16 formed at the juncturebetween the smaller and the larger inner diameter engages a bead 17formed on the layer 2. In addition to or in lieu of this arrangement,the juxtaposed surfaces of the layers 2 and 10 may be provided withprojections 18 (only one shown) which serve to maintain these layers atthe desired spacing, to thus create and maintain the gap 11.

As has been previously pointed out, the novel article has beenillustrated in the form of a distributor cap, but is not limited to thisapplication. It could as well be an ignition coil housing or a partthereof, for example, a closure cap for such a housing, or be used instill a different form and for a still different application.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofapplications differing from the types described above.

While the invention has been illustrated and described as embodied in adistributor cap, it is not intended to be limited to the details shown,since various modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims What is claimed as new and desired to be protected byLetters Patent is set forth in the appended:

l. A hollow insulating member having an open end and a closed end,particularly a distributor cap adapted to receive at least onecurrent-conducting lead connected to the ignition system of a combustionengine, comprising a wall having a first layer composed of anelectrically insulating substance, a second layer composed of athermally insulating material, one of said layers being an outer layerand surrounding at least a portion of the other of said layers which isan inner layer, said wall having at least one body of air entrappedtherein; a bead located on an outer surface of the inner layer of saidwall, a shoulder located on an inner surface of the outer layer of saidwall engaging said bead, so as to at least in part connect said innerlayer to said outer layer, and a plurality of tubular projectionsextending from said closed end and each adapted to receive acurrent-conducting lead.

2. An article as defined in claim 1, whereinrsaid layers are fast withone another.

3. An article as defined in claim 1, wherein said one layer is saidsecond layer.

4. An article as defined in claim 3, said second layer having an outersurface; and wherein said outer surface is substantially non-porous.

S. An article as defined in claim 3, wherein said material is an elasticmaterial.

6. An article as defined in claim 5, wherein said elastic material is afoam material having cells wherein said body of air is entrapped.

7. An article as defined in claim 5, wherein said first layer has firstouter dimensions, and said second layer has second inner dimensionssmaller than the corresponding ones of said first outer dimensions sothat said first layer maintains said second layer in an expanded stateand causes the latter to bear elastically against said first layer.

8. An article as defined in claim 1, wherein said material is a foammaterial having cells wherein said body of air is entrapped.

9. An article as defined in claim 8, wherein said foam material is ahard foam.

10. An article as defined in claim 9, wherein said hard foam is aclosed-cell foam.

11. An article as defined in claim 9, wherein said hard foam ispolyurethane foam.

12. An article as defined in claim 1, wherein said first and secondlayers are spaced apart over at least part of said portion and definewith one another a gap in which air is entrapped.

13. An article as defined in claim 12; and further comprising spacingmeans intermediate said first and second layers for spacing the samefrom each other to thereby provide said gap.

14. An article as defined in claim 1, wherein said second layer is of arigid synthetic resin.

15. An article as defined in claim 1, wherein said first and secondlayers are releasably connected with one another.

1. A hollow insulating member having an open end and a closed end,particularly a distributor cap adapted to receive at least onecurrent-conducting lead connected to the ignition system of a combustionengine, comprising a wall having a first layer composed of anelectrically insulating substance, a second layer composed of athermally insulating material, one of said layers being an outer layerand surrounding at least a portion of the other of said layers which isan inner layer, said wall having at least one body of air entrappedtherein; a bead located on an outer surface of the inner layer of saidwall, a shoulder located on an inner surface of the outer layer of saidwall engaging said bead, so as to at least in part connect said innerlayer to said outer layer, and a plurality of tubular projectionsextending from said closed end and each adapted to receive acurrentconducting lead.
 2. An article as defined in claim 1, whereinsaid layers are fast with one another.
 3. An article as defined in claim1, wherein said one layer is said second layer.
 4. An article as definedin claim 3, said second layer having an outer surface; and wherein saidouter surface is substantially non-porous.
 5. An article as defined inclaim 3, wherein said material is an elastic material.
 6. An article asdefined in claim 5, wherein said elastic material is a foam materialhaving cells wherein said body of air is entrapped.
 7. An article asdefined in claim 5, wherein said first layer has first outer dimensions,and said second layer has second inner dimensions smaller than thecorresponding ones of said first outer dimensions so that said firstlayer maintains said second layer in an expanded state and causes thelatter to bear elastically against said first layer.
 8. An article asdefined in claim 1, wherein said material is a foam material havingcells wherein said body of air is entrapped.
 9. An article as defined inclaim 8, wherein said foam material is a hard foam.
 10. An article asdefined in claim 9, wherein said hard foam is a closed-cell foam.
 11. Anarticle as defined in claim 9, wherein said hard foam is polyurethanefoam.
 12. An article as defined in claim 1, wherein said first andsecond layers are spaced apart over at least part of said portion anddefine with one another a gap in which air is entrapped.
 13. An articleas defined in claim 12; and further comprising spacing meansintermediate said first and second layers for spacing the same from eachother to thereby provide said gap.
 14. An article as defined in claim 1,wherein said second layer is of a rigid synthetic resin.
 15. An articleas defined in claim 1, wherein said first and second layers arereleasably connected with one another.